1902.] Longitudinal Magnetic Field on Internal Viscosity. 295 



unstable conditions of magnetic forces, a state of things which could 

 only be brought about with the assistance of forces independent of 

 magnetic action — forces which there is otherwise good reason to 

 believe do not exist to anything like the degree which would be 

 necessary. There are other reasons for believing that in the un- 

 magnetised metal the elementary magnets have a perfectly orderly 

 arrangement in closed chains, each of which may be composed of a 

 large group of molecules of the substance. These molecules, when the 

 substance is unmagnetised, form a closely coherent arrangement which 

 is broken up into an entirely different collocation under the influence 

 of an externally applied magnetic field. Thus if the wire of the 

 unmagnetised material perform torsional oscillations, the relative 

 motions of the parts of the material will naturally be affected by the 

 internal forces existing between the parts, and by the arrangement of 

 the parts in more or less distinct chains or groups. It is reasonable to 

 suppose that the effect of magnetisation being to entirely alter these 

 internal magnetic forces, and to break up and rearrange the groups of 

 elementary magnets, will be also to alter considerably the internal 

 friction shown by the material. With this idea in view, we have 

 subjected wires of iron, nickel, and steel to longitudinal magnetising 

 forces, while they were compelled to perform torsional oscillations 

 round their axes, and have observed the rate of subsidence of these 

 oscillations with magnetising forces of different values, the amounts of 

 which will be found stated in curves illustrative of the results obtained. 

 The effects of the fields were found to be considerable in amount and 

 very curious in character. For example, in the case of iron, as the 

 material was more intensely magnetised, the rate of subsidence of the 

 oscillations continually diminished; on the other hand, with wires of 

 nickel in the state in which they were received from the maker, the 

 effect was to increase the rate of subsidence until a certain value of the 

 magnetising force was reached, after which the rate of subsidence 

 diminished with further increase of the magnetising force. These 

 results were modified considerably by alteration in the state of the 

 material, produced by drawing the wires through a draw-plate. 



Since the completion of the experiments described in this paper, we 

 have become aware of a paper by Mr. Herbert Tomlinson, on the 

 subject of the effect of magnetisation on the internal viscosity of 

 iron.* The results obtained by Mr. Tomlinson, show an increase of 

 viscosity produced by a field of 35 units, which is contrary to 

 the effects described below. But the extreme amplitude in Mr. 

 Tomlinson's experiments was only 10° for a wire 1 metre long, as 

 against 90° in our experiments ; and as we have pointed out below, the 

 effect seems to depend in an important way upon the amplitude, though 



* ' Phil. Trans./ A, vol. 179, 1888. 



